C# | Check if a HashSet is a superset of the specified collection

Last Updated : 11 Jul, 2025

Sure, here's an example code that demonstrates using the IsSupersetOf method to check if a HashSet<string> is a superset of a List<string> and then printing out a message indicating the result:

using System;
using System.Collections.Generic;

public class Program
{
    public static void Main()
    {
        // create a HashSet of strings
        HashSet<string> set = new HashSet<string> { "apple", "banana", "cherry", "date" };

        // create a List of strings to check against the HashSet
        List<string> list = new List<string> { "apple", "banana" };

        // check if the HashSet is a superset of the List
        bool isSuperset = set.IsSupersetOf(list);

        // print out a message indicating the result
        if (isSuperset)
        {
            Console.WriteLine("The HashSet is a superset of the List.");
        }
        else
        {
            Console.WriteLine("The HashSet is not a superset of the List.");
        }
    }
}

Output

The HashSet is a superset of the List.

A HashSet is an unordered collection of the unique elements. It comes under System.Collections.Generic namespace. It is used in a situation where we want to prevent duplicates from being inserted in the collection. As far as performance is concerned, it is better in comparison to the list. HashSet<T>.IsSupersetOf(IEnumerable) method is used to check whether a HashSet object is a superset of the specified collection or not.

Syntax:

mySet1.IsSupersetOf(mySet2);

Here, mySet1 and mySet2 are the two HashSets.

Return Value: This method returns True if the HashSet object is a superset of another subset otherwise it returns False.

Exception: This method will give ArgumentNullException if the HashSet is null.

Below given are some examples to understand the implementation in a better way:

Example 1:

CSHARP

// C# code to Check if a HashSet is a
// superset of the specified collection
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet of strings
        HashSet<string> mySet1 = new HashSet<string>();

        // Inserting elements in HashSet
        mySet1.Add("Geeks");
        mySet1.Add("GeeksQuiz");

        // Creating a HashSet of strings
        HashSet<string> mySet2 = new HashSet<string>();

        // Inserting elements in HashSet
        mySet2.Add("DS");
        mySet2.Add("C++");
        mySet2.Add("Java");
        mySet2.Add("JavaScript");
        mySet2.Add("GeeksQuiz");
        mySet2.Add("Geeks");

        // Check if a HashSet is a superset
        // of the specified collection
        // It should return true as HashSet mySet2
        // is superset of HashSet mySet1
        Console.WriteLine(mySet2.IsSupersetOf(mySet1));
    }
}

Example 2:

CSHARP

// C# code to Check if a HashSet is a
// superset of the specified collection
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet of integers
        HashSet<int> mySet1 = new HashSet<int>();

        // Inserting elements in HashSet
        mySet1.Add(2);
        mySet1.Add(3);
        mySet1.Add(4);
        mySet1.Add(5);

        // Creating a HashSet of integers
        HashSet<int> mySet2 = new HashSet<int>();

        // Inserting elements in HashSet
        mySet2.Add(3);
        mySet2.Add(4);
        mySet2.Add(5);
        mySet2.Add(6);

        // Check if a HashSet is a superset
        // of the specified collection
        // It should return false as HashSet mySet2
        // is not a superset of HashSet mySet1
        Console.WriteLine(mySet2.IsSupersetOf(mySet1));
    }
}